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 A053067 a(n) = concatenation of next n numbers (omit leading 0's). 25
 1, 23, 456, 78910, 1112131415, 161718192021, 22232425262728, 2930313233343536, 373839404142434445, 46474849505152535455, 5657585960616263646566, 676869707172737475767778, 79808182838485868788899091, 9293949596979899100101102103104105, 106107108109110111112113114115116117118119120 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Concatenation of the integers from A000124(n-1) up to and including A000217(n). - R. J. Mathar, Aug 30 2013 The second term is a prime. When is the next prime, if there is another? - N. J. A. Sloane, Dec 16 2016 REFERENCES Felice Russo, A set of new Smarandache functions, sequences and conjectures in number theory, American Research Press 2000. LINKS FORMULA a(n) = n^2/2 + n/2 + Sum_{k=1..n-1} (n^2/2 + n/2 - k)*10^Sum{j=0..k-1} floor(1 + log_10(n^2/2 + n/2 - j)). - Paolo P. Lava, Dec 16 2008 MAPLE P:=proc(i) local a, k, j, n; for n from 1 by 1 to i do a:=n^2/2+n/2+sum('(n^2/2+n/2-k)*10^sum('floor(1+evalf(log10(n^2/2+n/2-j)))', 'j'=0..k-1)', 'k'=1..n-1); print(a); od; end: P(100); # Paolo P. Lava, Dec 16 2008 MATHEMATICA Table[FromDigits[Flatten[IntegerDigits/@Range[(n(n-1))/2+1, (n(n+1))/2]]], {n, 20}] (* Harvey P. Dale, Jan 23 2016 *) PROG (PARI) a(n) = my(s = ""); for (i=n*(n-1)/2 + 1, n*(n+1)/2, s = concat(s, Str(i)); ); eval(s); \\ Michel Marcus, Aug 11 2017 CROSSREFS A subsequence of A035333. For primes in latter, see A052087. See A279610 for a variant. Sequence in context: A001369 A007923 A080479 * A036906 A134733 A095256 Adjacent sequences:  A053064 A053065 A053066 * A053068 A053069 A053070 KEYWORD easy,base,nonn AUTHOR Felice Russo, Feb 25 2000 EXTENSIONS More terms from James A. Sellers, Feb 28 2000 More terms from Michel Marcus, Aug 11 2017 STATUS approved

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Last modified October 23 03:21 EDT 2019. Contains 328335 sequences. (Running on oeis4.)